Published Version

Abstract

Plasmonic nanoclusters, an ordered assembly of coupled metallic
nanoparticles, support unique spectral features known as Fano
resonances due to the coupling between their subradiant and
superradiant plasmon modes. Within the Fano resonance, absorption
is significantly enhanced, giving rise to highly localized, intense
near fields with the potential to enhance nonlinear optical
processes. Here, we report a structure supporting the coherent
oscillation of two distinct Fano resonances within an individual
plasmonic nanocluster. We show how this coherence enhances the
optical four-wave mixing process in comparison with other doubleresonant
plasmonic clusters that lack this property. A model that
explains the observed four-wave mixing features is proposed,
which is generally applicable to any third-order process in plasmonic
nanostructures. With a larger effective susceptibility χ (3) relative to
existing nonlinear optical materials, this coherent double-resonant
nanocluster offers a strategy for designing high-performance thirdorder
nonlinear optical media.